In recent years, one of the remarkable developments in cement production technology is the technical development of reducing the heat quantity required for burning a cement clinker (referred to as “clinker”, hereinafter). That is, there has been a change in burning technology, i.e. it has switched from a wet-burning method, which includes adding water to a mixed raw material to be uniformed, and thereafter burning the resultant mixture, thereby necessitating a large heat quantity required for burning, to a dry-burning method, which includes drying cement raw material by blowing hot air, and then crushing the raw material, and thereafter burning the raw material, so as to reduce the heat quantity required for burning, and further it has reached the development of a new-suspension type burning method, which includes calcining a mixed raw material by a preheater in advance, and placing the resultant calcined raw material into a rotary kiln (referred to as “kiln”, hereinafter) so as to further reduce the heat quantity required for burning.
Thereafter, as a technology for further reducing heat quantity required for burning, (1) a method of (non-patent document 1) changing the main chemical composition of a mixed raw material, and (2) a method of using a flux (non-patent document 1) have been developed.
The method (1) includes changing the contents of alumina, iron, sulfur, etc., to increase the quantity of a liquid phase at the time of burning, so as to ease to generate clinker even at a relatively low temperature.
The method (2) includes adding a flux such as fluorites (calcium fluoride), which promotes the burning reaction to cement raw materials.
[Non-patent document 1] H. F. W. Taylor, Cement Chemistry, U.K., ACADEMIC PRESS LIMITED, 1990, (1) method of changing the main chemical composition of compounding raw materials, page 80, (2) a method using a flux, p 93.